(1) Field of the Invention
This invention relates to a conductive film including a conductive coating layer and a method for producing the same.
(2) Description of the Prior Art
Conductive film, inter alia, transparent conductive film is widely used as, for example, a base material for electrophotographic recordings, a base material for electrostatic photographic recordings, transparent electrodes for thin liquid crystal displays, transparent electrodes for distributed electroluminescence displays, transparent electrodes for touch panels, clean rooms, meter windows, antistatic film for VTR tape, transparent heaters, and the like.
Conventionally used transparent conductive films are various kinds of semiconductor film-type conductive films that include ITO (Indium Tin Oxide) film, tin oxide film doped with antimony, CTO (Cadmium Tin Oxide) film, copper iodide film, titanium oxide film, zirconium oxide film, and the like. Of such semiconductor film-type conductive films, ITO film exhibits the most excellent transparency and conductivity. The formation of tin oxide film requires that the base be heated to a high temperature, resulting in its not being usable for polymeric film. CTO film has a small energy gap or an absorption edge on the long wavelength side compared with ITO film, and it is yellowish with an increased thickness. Copper iodide film, titanium oxide film, and zirconium oxide film are inferior in transparency and conductivity to such films.
The semiconductor film-type conductive films are generally prepared by vapor deposition and the like. Unfortunately this requires large-scale facilities, resulting in a significant increase in the manufacturing cost.
A method for manufacturing such a semiconductor film at a low cost is proposed which comprises the steps of previously subjecting a polymeric film base to a prime-coating treatment to form a prime-coating layer and causing a surface of the so-formed prime-coating layer to absorb a semiconductive compound, resulting in the formation of a transparent conductive film while improving adhesion of a conductive layer to the base and upper layer, as disclosed in JP-B No. 9984/1973. (The term "JP-B"means an examined Japanese patent publication.)
The conventional prime-coating described above was carried out using a swellable and electrically-insulating polymeric material exhibiting adhesion to a base. Unfortunately, this failed to cause the prepared transparent conductive film to exhibit satisfactory conductivity, although it was improved in adhesion and transparency.